U.S. patent number 7,945,361 [Application Number 10/563,370] was granted by the patent office on 2011-05-17 for method and system for determining a tyre load during the running of a motor vehicle.
This patent grant is currently assigned to Pirelli Pneumatici S.p.A.. Invention is credited to Daniele Arosio, Massimo Brusarosco, Federico Mancosu.
United States Patent |
7,945,361 |
Brusarosco , et al. |
May 17, 2011 |
Method and system for determining a tyre load during the running of
a motor vehicle
Abstract
A method for determining a load exerted on a tire, fitted on a
vehicle, during running of the vehicle on a rolling surface, is
disclosed. The method includes acquiring a first signal comprising
a first signal portion representative of a radial deformation;
measuring an amplitude of the radial deformation in the first
signal portion; estimating a rotation speed of the tire
corresponding to the radial deformation; estimating an inflation
pressure of the tire corresponding to the radial deformation; and
deriving the load exerted on the tire from the amplitude, the
rotation speed, and the inflation pressure. The first signal
portion is representative of the radial deformation to which a
first tread area portion of the tire is subjected during passage of
the first tread area portion through a contact region between the
tire and the rolling surface. A system for determining the load
exerted on the tire is also disclosed.
Inventors: |
Brusarosco; Massimo (Milan,
IT), Mancosu; Federico (Milan, IT), Arosio;
Daniele (Milan, IT) |
Assignee: |
Pirelli Pneumatici S.p.A.
(Milan, IT)
|
Family
ID: |
34042657 |
Appl.
No.: |
10/563,370 |
Filed: |
July 4, 2003 |
PCT
Filed: |
July 04, 2003 |
PCT No.: |
PCT/EP03/07185 |
371(c)(1),(2),(4) Date: |
May 26, 2006 |
PCT
Pub. No.: |
WO2005/005950 |
PCT
Pub. Date: |
January 20, 2005 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20070010928 A1 |
Jan 11, 2007 |
|
Current U.S.
Class: |
701/36; 340/683;
340/444; 702/42; 340/442 |
Current CPC
Class: |
G01G
19/025 (20130101); B60C 23/064 (20130101); B60C
23/06 (20130101); G01B 21/12 (20130101); G16Z
99/00 (20190201); G06F 17/40 (20130101) |
Current International
Class: |
G01L
1/00 (20060101) |
Field of
Search: |
;701/36,70
;340/444,442,445,683,870 ;73/146,629,146.2,488,514.34,783
;303/148,149 ;152/415,152.1 ;702/42 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
39 16 176 |
|
Nov 1990 |
|
DE |
|
1 293 362 |
|
Mar 2003 |
|
EP |
|
WO 03/016115 |
|
Feb 2003 |
|
WO |
|
Primary Examiner: To; Tuan C
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
Claims
The invention claimed is:
1. A method for determining a load exerted on a tyre, fitted on a
vehicle, during running of the vehicle on a rolling surface, the
method comprising: acquiring a first signal comprising a first
signal portion representative of a radial deformation; measuring an
amplitude of the radial deformation in the first signal portion;
estimating a rotation speed of the tyre corresponding to the radial
deformation; estimating an inflation pressure of the tyre
corresponding to the radial deformation; providing characteristic
functions describing an expected radial-deformation amplitude
versus rotation speed that correspond to predetermined conditions
of load exerted on the tyre and inflation pressure; and deriving
the load exerted on the tyre from the amplitude, the rotation
speed, and the inflation pressure; wherein the first signal portion
is representative of the radial deformation to which a first tread
area portion of the tyre is subjected during passage of the first
tread area portion through a contact region between the tyre and
the rolling surface, wherein measuring the amplitude of the radial
deformation comprises measuring a difference between: a maximum
value of the first signal in the first signal portion, and a
minimum value of the first signal in the first signal portion, and
wherein deriving the load exerted on the tyre comprises:
identifying a set of characteristic functions corresponding to the
estimated inflation pressure; and determining, from the set of
characteristic functions, a corresponding set of expected
radial-deformation amplitudes corresponding to the estimated
rotation speed.
2. The method of claim 1, wherein the first signal comprises a
radial acceleration signal.
3. The method of claim 1, further comprising: low-pass filtering
the first signal before measuring the amplitude of the radial
deformation.
4. The method of claim 1, wherein estimating the rotation speed of
the tyre comprises: measuring an average value of the first signal
in a second signal portion; wherein a time period associated with
the second signal portion does not overlap a time period associated
with the first signal portion.
5. The method of claim 1, wherein estimating the rotation speed of
the tyre comprises measuring an average value of the first signal
corresponding to an entire revolution of the tyre.
6. The method of claim 1, further comprising: acquiring a second
signal representative of a radial acceleration to which a second
tread area portion of the tyre is subjected.
7. The method of claim 6, wherein estimating the rotation speed of
the tyre comprises: measuring a value of the second signal during
passage of the first tread area portion through the contact region
between the tyre and the rolling surface.
8. The method of claim 1, further comprising: sampling the first
signal at a frequency greater than or equal to 5 kHz before
measuring the amplitude of the radial deformation.
9. The method of claim 8, further comprising: sampling the first
signal at a frequency greater than or equal to 7 kHz before
measuring the amplitude of the radial deformation.
10. The method of claim 1, wherein the characteristic functions
comprise polynomial functions.
11. The method of claim 1, wherein deriving the load exerted on the
tyre further comprises: comparing the measured radial-deformation
amplitude with any one of the set of expected radial-deformation
amplitudes in order to identify a closest expected
radial-deformation amplitude; and establishing the load exerted on
the tyre based on the closest expected radial-deformation
amplitude.
12. A method of controlling a vehicle having at least one tyre
fitted on the vehicle, the method comprising: determining a load
exerted on the at least one tyre; passing the determined load to a
vehicle control system of the vehicle; and adjusting at least one
parameter in the vehicle control system based on the determined
load; wherein the load exerted on the at least one tyre is
determined by a method comprising: acquiring a first signal
comprising a first signal portion representative of a radial
deformation; measuring an amplitude of the radial deformation in
the first signal portion; estimating a rotation speed of the at
least one tyre corresponding to the radial deformation; estimating
an inflation pressure of the at least one tyre corresponding to the
radial deformation; providing characteristic functions describing
an expected radial-deformation amplitude versus rotation speed that
correspond to predetermined conditions of load exerted on the tyre
and inflation pressure; and deriving the load exerted on the at
least one tyre from the amplitude, the rotation speed, and the
inflation pressure; wherein the first signal portion is
representative of the radial deformation to which a first tread
area portion of the at least one tyre is subjected during passage
of the first tread area portion through a contact region between
the at least one tyre and a rolling surface, wherein measuring the
amplitude of the radial deformation comprises measuring a
difference between: a maximum value of the first signal in the
first signal portion, and a minimum value of the first signal in
the first signal portion, and wherein deriving the load exerted on
the tyre comprises: identifying a set of characteristic functions
corresponding to the estimated inflation pressure; and determining,
from the set of characteristic functions, a corresponding set of
expected radial-deformation amplitudes corresponding to the
estimated rotation speed.
13. The method of claim 12, wherein the vehicle control system
comprises: a brake control system; wherein adjusting the at least
one parameter comprises adjusting a braking force on the at least
one tyre.
14. The method of claim 12, wherein the vehicle control system
comprises: a steering control system; wherein adjusting the at
least one parameter comprises selecting a maximum variation allowed
from steering commands.
15. The method of claim 12, wherein the vehicle control system
comprises: a suspension control system; wherein adjusting the at
least one parameter comprises adjusting stiffness of a suspension
spring associated with the at least one tyre.
16. The method of claim 12, wherein the vehicle comprises at least
one tyre fitted on each of two opposite sides of the vehicle,
wherein the vehicle control system comprises an active roll control
system, and wherein adjusting the at least one parameter comprises
compensating an unequal load distribution between the at least one
tyre fitted on each of two opposite sides of the vehicle.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a national-phase entry under 35 U.S.C.
.sctn.371 from International Application No. PCT/EP2003/007185,
filed Jul. 4, 2003, in the European Patent Office, the content of
which is relied upon and incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a system for
determining a vertical load to which a tyre mounted on a vehicle is
subjected, during running of the vehicle.
2. Description of the Related Art
Inflation pressure is a convenient measurement to make on a tyre
fitted on a vehicle wheel and it is becoming a standard by which
tyres are monitored. Tyre load, i.e., the supported weight, is a
more difficult measurement but, unlike pressure, is a direct
measurement of tyre stress. Tyres are selected for a particular
vehicle based on the physical strength of their structure and/or
material, as well as on the normal range of vehicle weight that
they should support at specified nominal temperature and pressure.
If the vehicle applies a load to a tyre in excess of the load range
for which the tyre has been designed, the tyre is subjected to
excessive stress and may fail or have its expected lifetime
shortened.
Furthermore, it has to be considered that tyre maintenance is
mainly based on the duty, by the vehicle driver, of maintaining
tyre pressure near a nominal value, defined by the vehicle and tyre
manufacturers. Although it is well known by the tyre industry that
the requisite pressure is dependent on the supported load, this
load-dependent pressure information is not provided to the driver,
since real-time load is unknown. As a result, should the load vary
from that assumed by the manufacturer, the tyres may be improperly
inflated. Since the requisite pressure increases with load, the
only option left is to assume the maximum load and specify a
pressure accordingly. However, this maximum pressure can: 1) give a
very hard ride; 2) reduce the tyre-to-road contact area available
for braking; 3) wear out the center of the tyre tread prematurely.
Thus, tyre load information is needed to properly inflate
tyres.
Moreover, vehicle electronic control systems, such as for example a
vehicle brake control system, a traction control system, an
anti-lock braking system, an electronic braking system, a steering
control system, an active roll control system, a vehicle stability
control system, may use information related to the tyre load, in
order to control actuators that move, control and stop the
vehicle.
This tyre information may be used within the vehicle, or it can be
used remotely, i.e. outside the vehicle. As the telematic
capability of vehicles increases, they are capable of wirelessly
communicating with a remote facility for monitoring the vehicle
health (diagnostics), for prediction of maintenance (prognostics),
and to monitor the vehicle as it passes on the road. The
information may be also historically important to understand the
cause of accidents.
U.S. Pat. No. 5,793,285 discloses a method and apparatus for
monitoring tyres on a vehicle, by continuously measuring the
distance between the associated vehicle axle (or a vehicle body
part rigidly connected thereto) and the road, while the vehicle is
in operation. From this measurement, the tyre deflection is
determined. According to the authors, the measured tyre deflection
represents a comparatively exact measure of the respective tyre
load. When the tyre deflection determined leaves a predetermined
desired range, a warning signal is transmitted.
PCT patent application no. WO 03/016115 discloses a method for
determining the charge or load exerted on a tyre of a motor vehicle
and/or for monitoring tyre pressure, wherein the pressure in each
tyre is detected during operation of the vehicle and the rotational
behavior of the individual wheels is observed. Load distribution
parameters are also determined by comparing the rotational behavior
and/or changes in said rotational behavior of the individual wheels
during given driving states, taking into account preset and/or
predetermined and/or learned variables. Tyre pressure and load
distribution parameters are used to determine the load or charge
exerted on the tyres and/or pressure loss. In one example, a
pressure-measuring system based on the use of pressure sensors
(such as TPMS=Tyre Pressure Measuring System), is used to determine
the tyre pressure, whilst characteristic variables representing the
load distribution are determined using a system based on an
evaluation of wheel speed data operating in the manner of a system
(Deflation Detecting System=DDS) used to determine conditions
relating to the dynamic rolling circumferences of the individual
tyres. Consequently, the function of detecting capacity utilization
can be set up using existing systems. In another example, the
number of revolutions of a front wheel is compared with the number
of revolutions of a rear wheel at the same vehicle speed or at
approximately the same vehicle speed (e.g. vehicle reference
speed), evaluated to obtain a load distribution characteristic
variable, and the value and/or the change in the load distribution
characteristic variables in defined driving situations is/are used
as a means of calculating the capacity utilization or load of the
tyres and/or the pressure loss.
US patent application no. 2003/0058118 discloses a vehicle and
vehicle tyre monitoring system, apparatus and method for
determining the load-induced deflection or deformation of a vehicle
tyre. Based thereon, deflection-related information, such as tyre
load, molar air content, total vehicle mass and distribution of
vehicle mass, are provided. The tyre deflection region or contact
region of the loaded tyre is detected by sensing the acceleration
of the rotating tyre by means of an accelerometer mounted on the
tyre, preferably on an inner surface such as the tread lining
thereof. As the tyre rotates and the accelerometer is off of the
contact region, a high centrifugal acceleration is sensed.
Conversely, when the accelerometer is on the contact region and not
rotating, a low acceleration is sensed. The deflection points
delimiting the contact region are determined at the points where
the sensed acceleration transitions between the high and low
values. From a measurement of the rotation rate of the tyre, of the
time between detections of the deflection points and from the tyre
radius, the contact length (contactLength) can be determined. In
order to determine the tyre load, the following formula is
suggested:
load=.alpha..times.treadWidth.times.contactLength.times.pressure+forceSid-
ewall where treadWidth is the width of the tread,
treadWidth.times.contactLength is the area of applied pressure,
forceSidewall is the effective resiliency of the tyre sidewall to
collapse, and .alpha. is a proportionality constant near to 1.
Alternatively, the load can be determined from a disclosed
relationship between air moles, pressure, temperature and contact
length, derived from the Ideal Gas Law.
According to the Applicant, the methods disclosed in the above U.S.
Pat. No. 5,793,285 and in the above PCT patent application no. WO
03/016115 may not give reliable real-time determinations of the
tyre load, since they are not based on measurements performed
directly on the tyre. Thus, they may suffer from an "averaging
effect", which can cause a loss of important tyre load data,
especially in rapidly varying conditions.
On the other hand, the approach disclosed in the above US patent
application no. 2003/0058118 is quite theoretical and could not fit
with a complex system such as a tyre. For example, considering the
rectangle treadWidth.times.contactLength as the area of applied
pressure is a strong approximation, as the contact area between the
tyre tread and the road is quite different from a rectangle.
Furthermore, the value forceSidewall is generally not determined
with high precision, so that a further approximation would be
included in the tyre load determination.
SUMMARY OF THE INVENTION
The Applicant has faced the problem of determining in real-time,
i.e. during the running of the vehicle, and in a reliable way, the
load to which a tyre fitted on the vehicle is subjected.
The Applicant has found that such problem can be solved by
measuring the amplitude of the deformation in radial direction to
which a portion of the tread area of the tyre is subjected when
such portion passes in correspondence of the contact region between
the tyre and the road, and by relating such amplitude to the
rotation speed and to the inflation pressure of the tyre.
Hereinafter, the deformation in radial direction will be referred
as "radial deformation". Such radial deformation can be detected,
for example, by means of a radial accelerometer secured to the
inner liner of the tyre.
In a first aspect, the invention relates to a method for
determining a load exerted on a tyre fitted on a vehicle during a
running of said vehicle on a rolling surface, the method comprising
the following steps: acquiring a first signal comprising a first
portion representative of a radial deformation to which a first
tread area portion of said tyre is subjected during passage of said
first tread area portion in a contact region between said tyre and
said rolling surface; measuring an amplitude of said radial
deformation in said first signal portion; estimating a rotation
speed and an inflation pressure of said tyre corresponding to said
radial deformation; deriving said tyre load from said amplitude,
said rotation speed and said inflation pressure.
Said first signal may comprise a radial acceleration signal. Said
step of measuring said amplitude can be performed by measuring a
difference between a maximum value of said first signal and a
minimum value of said first signal in said first signal
portion.
For the purposes of the present invention, the expression
"estimating a rotation speed and an inflation pressure of said tyre
corresponding to said radial deformation" may include either a
measurement from which the tyre inflation pressure value and/or the
rotation speed value in the time interval in which the radial
deformation of the first tread portion occurred can be inferred
(even if such measurement is performed in a subsequent time
interval), or a measurement of the tyre inflation pressure value
and/or of the rotation speed value performed in real time, i.e.
during the occurrence of the radial deformation of the first tread
area portion.
The method may further comprise, before said step of measuring said
amplitude, a further step of low-pass filtering said first
signal.
Said step of estimating said rotation speed of the tyre may
comprise measuring an average value of said first signal in a
second signal portion, outside from said first signal portion.
Alternatively, said step of estimating said rotation speed of the
tyre may comprise measuring an average value of said first signal
in a whole turn of said tyre.
In a preferred embodiment, the method further comprises a step of
acquiring a second signal representative of a radial acceleration
to which a second tread area portion of said tyre is subjected. In
such preferred embodiment, said step of estimating said rotation
speed of the tyre may comprise measuring a value of said second
signal during said passage of said first tread area portion in said
contact region between said tyre and a rolling surface.
The method may further comprise, before said step of measuring said
amplitude, a further step of sampling said first signal at a
frequency of at least 5 kHz, preferably of at least 7 kHz.
The method may further comprise a step of providing characteristic
functions describing an expected radial deformation amplitude
versus rotation speed, corresponding to predetermined conditions of
tyre load and inflation pressure. Said characteristic functions may
comprise polynomial functions.
Preferably, said step of deriving said tyre load may comprise:
identifying a set of characteristic functions corresponding to said
estimated inflation pressure; determining, from said set of
characteristic functions, a corresponding set of expected radial
deformation amplitudes corresponding to said estimated rotation
speed.
More preferably, said step of deriving said tyre load may further
comprise: comparing said measured radial deformation amplitude with
any one of said set of expected radial deformation amplitudes, in
order to identify a closer expected radial deformation amplitude;
determining said tyre load based from said closer expected radial
deformation amplitude.
In a second aspect, the invention relates to a method of
controlling a vehicle having at least one tyre fitted thereon,
comprising: determining a load exerted on said tyre by a method
according to the first aspect; passing said determined load to a
vehicle control system of the vehicle; adjusting at least one
parameter in said vehicle control system based on said determined
load.
The vehicle control system may comprise a brake control system, and
said step of adjusting at least one parameter may comprise
adjusting a braking force on said tyre.
Alternatively or in combination, the vehicle control system may
comprise a steering control system, and said step of adjusting at
least one parameter may comprise selecting a maximum variation
allowed from steering commands.
Alternatively or in combination, the vehicle control system may
comprise a suspension control system, and said step of adjusting at
least one parameter may comprise adjusting a stiffness of a
suspension spring associated to said tyre.
Typically, the vehicle comprises at least one tyre fitted on its
right and at least one tyre fitted on its left. Alternatively to or
in combination with the previous embodiments, the vehicle control
system may comprise an active roll control system, and said step of
adjusting at least one parameter comprises compensating an unequal
load distribution between said left fitted tyre and said right
fitted tyre.
In a third aspect, the invention relates to a system for
determining a load exerted on a tyre fitted on a vehicle during a
running of said vehicle on a rolling surface, the system
comprising: a measuring device adapted to acquire a signal
representative of a deformation to which a first tread area portion
of said tyre is subjected during passage of said first tread area
portion in a contact region between said tyre and said rolling
surface; a pressure sensor adapted to sense an inflation pressure
of said tyre; a device for estimating a rotation speed of said
tyre; at least one processing unit being adapted to determine an
amplitude of said radial deformation in said first signal portion,
and to derive said tyre load from said amplitude, said rotation
speed and said inflation pressure.
In a preferred embodiment, said measuring device comprises a radial
accelerometer.
The device for estimating the rotation speed of said tyre may be
the same processing unit.
The system of the invention may further comprise a filtering device
adapted for low-pass filtering said signal.
The measuring device may further comprise a sampling device adapted
to sample said signal at a frequency of at least 5 kHz, preferably
of at least 7 kHz.
At least one memory can be associated to said processing unit. Said
at least one memory may comprise pre-stored characteristic
functions describing an expected radial deformation amplitude
versus rotation speed, corresponding to predetermined conditions of
tyre load and inflation pressure. Said functions may comprise
polynomial functions.
Said at least one memory may further comprise pre-stored
instructions for said processing unit. Said pre-stored instructions
may comprise at least a first set of instructions being adapted to:
identify a set of characteristic functions corresponding to a
sensed inflation pressure; determine, from said set of
characteristic functions, a corresponding set of expected radial
deformation amplitudes corresponding to said estimated rotation
speed.
Said pre-stored instructions may further comprise at least a second
set of instructions being adapted to: compare said determined
radial deformation amplitude with any one of said set of expected
radial deformation amplitudes, in order to identify a closer
expected radial deformation amplitude; determine said tyre load
based from said closer expected radial deformation amplitude.
Said measuring device may be included in a sensor device located in
a tread area portion of said tyre. Preferably, said sensor device
may be disposed substantially in correspondence of an equatorial
plane of the tyre.
Preferably, said sensor device may be secured to an inner liner of
the tyre. In this embodiment, a damping element may be interposed
between said sensor and said inner liner.
The sensor may further comprise a power source. Said power source
may comprise a battery or, preferably, a self-powering device,
being adapted to generate electrical power as a result of
mechanical stresses undergone by said sensor device during running
of said vehicle. Said self-powering device may, for example,
comprise a piezoelectric element. Furthermore, said self-powering
device may comprise an electrical storage circuit, typically
comprising a resistor and a capacitor.
Preferably, the processing unit is included within said sensor
device.
Typically, the sensor device further includes a transmitting
device. Said transmitting device may be operatively connected to a
first antenna.
The system according to the invention may further comprise a fixed
unit located on the vehicle, comprising a receiving device for
receiving data from said sensor device. Said receiving unit
typically comprises a second antenna.
Said first antenna and said second antenna are typically adapted
for data transmission at a frequency comprised between 400 and 450
MHz.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the present invention will be
better illustrated by the following detailed description, herein
given with reference to the enclosed drawings, in which:
FIG. 1 shows a cross section of a tyre according to the invention,
including a sensor device;
FIG. 2 shows a diagram of a fixed unit included in a system
according to the invention;
FIG. 3 shows a diagram of a sensor device included in a tyre
according to the invention;
FIG. 4 shows a series of radial acceleration curves obtained at
different tyre rotation speeds;
FIGS. 5a and 5b exemplarily disclose two sets of curves of radial
deformation peak amplitude versus tyre rotation speed,
corresponding to different tyre loads, respectively for a first and
second value of tyre inflation pressure;
FIGS. 6a and 6b schematically show a radial deformation signal and
a filtered radial deformation signal, respectively;
FIG. 7 shows further sets of curves of radial deformation peak
amplitude versus tyre rotation speed, corresponding to different
tyre loads.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
FIG. 1 shows a cross section of a wheel comprising a tyre 11 and a
supporting rim 12. The tyre 11 shown in FIG. 1 is of a type
conventionally known as "tubeless", i.e. it does not include an
inner tube. This tyre can be inflated by means of an inflation
valve 13 positioned, for example, on the channel of the said rim
12.
The tyre 11 includes a carcass 16, terminating in two beads 14 and
14', each formed along an inner circumferential edge of the carcass
16, for fixing the tyre 11 to the corresponding supporting rim 12.
The beads 14, 14' comprise respective reinforcing annular cores 15
and 15', known as bead cores. The carcass 16 is formed by at least
one reinforcing ply, including textile or metallic cords, extending
axially from one bead 14 to the other 14' in a toroidal profile,
and having its ends associated with a respective bead core 15 and
15'. In tyres of the type known as radial, the aforesaid cords lie
essentially in planes containing the axis of rotation of the tyre.
An annular structure 17, known as belt structure, is placed in a
radially external position with respect to the carcass 16.
Typically, the belt structure 17 includes one or more strips of
elastomeric material incorporating metal and/or textile cords,
overlapping with each other. A tread band 18 of elastomeric
material is wound around the belt structure 17 and impressed with a
relief pattern for the rolling contact of the tyre with the ground.
Two sidewalls 19 and 19' of elastomeric material, each extending
radially outwards from the outer edge of the corresponding bead 14
and 14', are also placed on the carcass 16 in axially opposed
lateral positions. In tubeless tyres the inner surface of the
carcass 16 is normally covered with a liner 111, i.e. with one or
more layers of air-impermeable elastomeric material. Other known
elements, such as for example bead fillers may be provided,
according to the specific design of the tyre 11.
A sensor device 3, that will be described in detail in the
remainder of the description, is included within the tyre 11. The
sensor device 3 is located in a portion of the tread area of the
tyre 11, i.e. the region of the tyre 11 axially extended between
the sidewalls of the tyre 11. Preferably, the sensor device is
disposed substantially in correspondence of the equatorial plane of
the tyre 11. In the preferred embodiment shown in FIG. 1, the
sensor device 3 is secured to the inner liner 111 of the tyre 11. A
fixing element 332 adheres both to the sensor device 3 and to the
inner liner 111. Suitable materials for the fixing element 332 may
include generally flexible rubbers, such as for example natural
rubber, or synthetic rubber, e.g. rubbers made from conjugated
dienes having from 4 to 10 carbon atoms such as poly-isoprene,
polybutadiene, styrene-butadiene rubber and the like. In preferred
embodiments, a material included in the fixing element 332 should
have a damping effect, in order to secure the fixing of the sensor
device 3 to the inner surface of the tyre by minimizing the
mechanical stresses exerted onto the fixing surface during use of
the tyre 11. Furthermore, a damping material reduces the
probability of damages to the sensor device 3 by preventing
transmission of the above stresses to the device. Suitable damping
materials may have a Shore A hardness (measured at 23.degree. C.
according to ASTM Standard D2240) of from about 1 to about 40, and
an elastic rebound (measured at 23.degree. C. according to ASTM
Standard D1054) lower than about 60. Cross-linked diene elastomers
or polyurethane gel materials may be adapted in order to fit with
these damping specifications. For improved adhesion between the
sensor device 3 and the tyre 11, it may be advantageous to
interpose a further adhesive element, for example a double-sided
adhesive film, between the fixing element 332 and the inner surface
of the tyre 11 and/or between the fixing element 332 and the sensor
device 3. An appropriate double-sided adhesive film may be the
Scotch.RTM. 300SL HI Strength, marketed by 3M. In alternative
embodiments, the sensor device 3 may be incorporated within the
structure of the tyre in the tread area, for example within the
tread band, or between the outer belt strip and the tread band.
In a preferred embodiment of the present invention (not shown), a
plurality of sensor devices are associated to a tyre 11. More
particularly, the sensor devices may be located in a
circumferential position spaced one from each other of
substantially the same angle. For example, three sensor devices may
be located within the tyre, circumferentially spaced from each
other of an angle of substantially 120.degree.. As far as the
securing of the plurality of the sensor devices to the tyre 11,
reference is made to what said above.
As it will be clarified in the following, the use of a plurality of
sensor devices allows to achieve more accuracy and reliability of
the measurements performed, as well as a better monitoring of the
tyre load during the entire wheel turn.
The sensor device 3 is adapted to communicate with a unit external
to the tyre 11. Such external unit will be referred in the
following as "fixed" unit. Typically, the fixed unit may be located
on the vehicle on which the tyre 11 is fitted. Alternatively or in
combination with a fixed unit located on the vehicle, a fixed unit
may be a hand-held unit usable by an operator, or a unit located
along a roadway (e.g. in a service station).
For example, FIG. 2 shows a block diagram of a fixed unit 2,
comprising a device for receiving from the sensor device 3 included
within the tyre 11. Preferably, the fixed unit 2 also comprises a
device for transmitting to said sensor device 3. The receiving
device may comprise a radio-frequency receiver 26 connected to a
first antenna 25, referred to below as the "fixed antenna".
Preferably, the receiving device also comprises an electrical
demodulator device 27. A memory 28, such as for example an EPROM,
can store the data received by the sensor device 3 and demodulated
by the demodulator 27. In preferred embodiments, the memory 28 is
associated to a central processing unit (CPU, not shown in FIG. 2),
in order to perform calculations from the data received by the
sensor device 3 and/or stored in the memory 28. The memory 28 may
also store historical logs of excessive tyre loads, pressure and/or
temperatures, possibly in combination with logs of the steps taken
by a vehicle control system in order to control the vehicle
behavior and/or of alarm messages displayed to the driver of the
vehicle. The transmission device preferably comprises an oscillator
circuit 23, which supplies a driver circuit 24 for the fixed
antenna 25. If the fixed unit 2 is located on the vehicle, the
electrical energy required to power the fixed unit 2 can be
supplied directly by the vehicle battery.
The sensor device 3, an exemplary block diagram of which is shown
in FIG. 3, comprises in general terms a device 31 for data
transmission to the said fixed unit and a measuring device 32
adapted to measure a radial deformation of the tread area portion
of the tyre 11 to which the sensor device 3 is associated. The
measuring device 32 may preferably comprise a radial accelerometer.
Such radial accelerometer should be capable of support and
correctly measure very high acceleration values, as the radial
acceleration supported by the tread area of the tyre may reach, at
high speed, values of 500-1000 g, wherein g is the gravity
acceleration. In an alternative embodiment, the measuring device
may comprise an extensometer, whose output signal gives a measure
of the flexion of the monitored tread area portion. The load to
which the tyre is subjected is determined by measuring the
amplitude of the radial deformation to which the tread area portion
corresponding to the position of the sensor device 3 is subjected.
For the purposes of the present invention, the expression "radial
deformation" may comprise either the actual tyre deflection (for
example measured in mm, or as a ratio to the tyre radius) to which
the monitored tread area portion is subjected, or the radial
acceleration to which the monitored tread area portion is
subjected. In order to perform a real-time determination of the
tyre load, the radial deformation should be detected with high
precision, preferably at any turn of the tyre. For this purpose,
and taking into account the frequency rotation of a rolling tyre
(particularly at high speed), the measuring device 32 preferably
includes a sampling device (not shown) capable of enabling the
reading of the sensed radial deformation signal at a frequency of
at least 5 kHz, more preferably at a frequency of at least 7 kHz,
so as to furnish a sampled signal thereof. In preferred
embodiments, the measuring device 32 may also include a pressure
sensor and/or a temperature sensor. However, pressure and
temperature measurements do not need a high frequency sampling: a
single measure per tyre turn may be sufficient. In alternative
embodiments, a pressure and/or a temperature sensor may also be
disposed externally of the sensor device 3, e.g. located within the
tyre valve. The sensor device 3 typically includes also an antenna
37, referred to below as the "mobile antenna", operatively
connected to said transmission device 31, for data transmission to
the fixed antenna of the fixed unit. Transmission from the mobile
antenna to the fixed antenna may occur at conventional telemetry
radio-frequencies, e.g. in a band comprised between 400 and 450 MHz
(for example at 418 MHz or 433 MHz).
The sensor device 3 may further include a processing unit (CPU) 34,
associated to a memory device 35. This memory device 35 may contain
re-writable memory locations in which information about the
measurements taken by the measuring device 32 can be stored.
Furthermore, it may also contain pre-stored instructions for the
processing unit 34, suitable for pre-processing the signals coming
from the measuring unit 32 before transmission, in order to reduce
the quantity of information sent out of the tyre 11. More
particularly, the deformation signal may be pre-processed in order
to detect characteristic points, such as for example maxima and
minima, the coordinates of which can be sent to the transmission
device 31 for transmission to the fixed unit. This allows to save
transmission bandwidth and required power for transmission.
Furthermore, a filtering device (not shown) may be interposed
between the measuring unit 32 and the processing unit 34, in order
to low-pass filter the deformation signal and discriminate the
useful signal from high-frequency noise caused by the interaction
between the tread band and the road. However, such filtering may be
provided by electronics included within the measuring device 32 or
as further pre-processing instruction stored within the memory
35.
A power source 33 allows to energize the sensor device 3. The
sensor device 3 may be powered by a battery. However, for a
real-time determination of the tyre load a great electrical power
consumption may be requested by the measuring device 32 (in
particular by a high frequency sampling device), by the processing
unit 34 and by the transmission device 31, so that a battery could
have short lifetime, as compared to the entire life of the tyre.
Thus, in preferred embodiments the power source 33 includes a
self-powering device, which generates electricity as a result of
the mechanical stresses to which said self-powering device is
subjected (for example, centrifugal force, or the deformations of
the liner, or movements due to traveling on uneven roads). As an
example, piezoelectric materials may be used in the self-powering
device for such purpose. The self-powering device also includes an
electrical energy storage circuit (not shown), typically including
a resistor and a capacitor. As a further alternative, the sensor
device 3 may be energized by the fixed unit by means of a suitable
receiving device (not shown), connected to the mobile antenna
31.
A device for distributing the electrical power 36 preferably
distributes appropriately the electrical power provided by the
power source 33 to said processing unit 34, to said memory device
35, to said device for transmitting 31 and to said measuring device
32, according to their requirements.
It has to be noticed that it is not necessary to include the
measuring device, the transmission portion to the fixed unit and
the control electronics within a single packaged sensor device. For
example, the control electronics and the transmission portion to
the fixed unit could be packaged in a separated device secured to
other parts of the tyre or of the wheel (e.g. the rim, or the
sidewall), associated by a wired or wireless (e.g. optical or by
radio-frequency) connection to a measuring device located in the
tread area portion of the tyre.
FIG. 4 shows, by way of example, the result of a series of
measurements performed by the Applicant by securing a radial
accelerometer to the inner liner of a tyre model Pirelli.RTM.
P6000.RTM. 195/65 R15, inflated at a pressure of 2.2 bar, with a
load of 3500 N. A rolling of the tyre was caused at different
speeds and the radial acceleration signal detected by the
accelerometer was correspondingly plotted. In FIG. 4, the rotation
angle R for a single turn around the tyre axis of the tread area
portion corresponding to the accelerometer position is reported in
abscissa. The angle ranges from 0.degree. to 360.degree., these two
extremes corresponding substantially to a radially opposite
position with respect to the contact region between the tyre and
the road (hereinafter contact patch). On the contrary, the position
around 180.degree. corresponds to the passage of the crown portion
monitored by the accelerometer under the contact patch. The radial
acceleration a sensed by the accelerometer is reported in ordinate,
as a multiple of g. Curve 41 refers to a traveling speed of 40
km/h, curve 42 refers to a traveling speed of 60 km/h, curve 43
refers to a traveling speed of 80 km/h, curve 44 refers to a
traveling speed of 100 km/h. As it can be seen, in correspondence
to the passage under the contact patch the level of radial
centrifugal acceleration sensed by the accelerometer increases
abruptly a first time, then drops to until substantially zero, and
then increases abruptly a second time. In other positions the
radial acceleration sensed by the accelerometer has an average
level related to the rotation speed of the rolling tyre: the higher
the speed, the higher the sensed acceleration. The curves of FIG. 4
show that when the tread area portion corresponding to the position
of the accelerometer begins and ends its passage under the contact
patch, such tread area portion is subjected to a strong radial
deformation (corresponding to the peaks shown by the curves),
whereas in other positions such tread area portion is not
practically subjected to deformations (corresponding to the
substantially zero acceleration value within the contact patch and
to the substantially constant acceleration value outside from the
contact patch).
By analyzing radial acceleration curves in different conditions of
rotation speed, load and inflation pressure, the Applicant has
observed that: a) the amplitude of the peaks representing the
radial deformation of the tread area portion increases with
increasing rotation speed of the tyre (i.e., the higher the speed,
the higher the peaks); b) at constant speed, the amplitude of the
peaks representing the radial deformation of the tread area portion
increases with increasing tyre load (i.e., the higher the load, the
higher the peaks); c) at constant speed, the amplitude of the peaks
representing the radial deformation of the tread area portion
decreases with increasing tyre inflation pressure (i.e., the higher
the pressure, the lower the peaks).
Summarizing the above results, the Applicant has plotted different
curves of radial deformation (peak) amplitude versus rotation
speed, corresponding to different tyre loads, on the same graph, at
constant inflation pressure. FIGS. 5a, 5b show two of such plots,
carrying curves of peak amplitude versus tyre rotation speed
increasing tyre loads (the arrow shown in the figures refers to
increasing tyre loads). FIGS. 5a, 5b relate to an inflation
pressure of 1.6 bar (FIG. 5a) and 2.2 bar (FIG. 5b). As each curve
represents a predetermined tyre load value, by knowing the rotation
speed and the inflation pressure, and by measuring the radial
deformation peak amplitude value, a unique curve representing a
tyre load value can be identified in the graph, i.e. the tyre load
can be estimated.
On the other hand, since a.sub.radial=V.sup.2/R or
a.sub.radial=.omega..sup.2R (wherein R is the radius of the tyre),
the average level of acceleration to which the tread area portion
corresponding to the position of the radial accelerometer is
subjected outside the contact patch increases with increasing
rotation speed, substantially without any dependency on the tyre
load and inflation pressure. This means that the rotation speed of
the tyre can be derived by measuring the average radial
acceleration level in the portion of the radial acceleration signal
corresponding to the outside of the contact patch, for any tyre
load and inflation pressure. Thus, advantageously, a signal
furnished by a radial accelerometer disposed in a tread area
portion of the tyre can give two of the parameters needed for
estimating the tyre load, i.e. the amplitude of the radial
deformation peak and the rotation speed. The third parameter, i.e.
the inflation pressure, can be provided by a conventional pressure
sensor. However, it has to be noticed that also the tyre rotation
speed may be provided by a separate device, such as for example by
a measurement performed in other parts of the vehicle, different
from the tyre (e.g., the wheel hub).
In a preferred method for determining the tyre load, each of the
curves shown in FIGS. 5a, 5b can be described by a fit function,
such as for example a polynomial fit function. For example, the
curves obtained at a pressure p and at different tyre loads q1, q2,
. . . qn can be described by parabolic fit functions:
.times..times..times..times..times..times..omega..times..times..times..ti-
mes..times..omega..times..times..times..times..times..times..times..times.-
.times..times..times..times..omega..times..times..times..times..times..ome-
ga..times..times..times..times..times..times..times..times..times..times..-
times..times..times..omega..times..times..times..omega..times..times..time-
s..times. ##EQU00001##
The values y.sub.--1(q, p, .omega.), . . . , y_n(q, p, .omega.)
calculated with equations [1] represent expected radial deformation
peak values, at given conditions of tyre load, pressure and
rotation speed.
In an initial step of characterization of a tyre, graphs similar to
those shown in FIGS. 5a and 5b can be plotted for the tyre at
predetermined inflation pressure values p1, p2 . . . pn,
predetermined tyre loads q1, q2, . . . . qn, and predetermined
rotation speeds, in order to find the sets of fit coefficients for
the above values of inflation pressure, i.e.
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times..times..times..times..times..times..times..times..times..time-
s..times..times..times..times..times..times..times..times..times..times..t-
imes..times..times..times..times..times..times..times..times..times..times-
..times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times..times..times..times..times..times..times..times..times..time-
s..times..times..times..times..times..times..times..times..times..times..t-
imes..times..times. ##EQU00002##
The fit coefficients [2], as well as the pressure values to which
they are related, can be stored within the memory included within
the sensor device 3 located in the tread area of the tyre. The
above described characterization of the tyre can be performed once
per tyre model, for example in indoor tests.
With reference to FIG. 6, during running of the tyre, a signal
representative of the radial acceleration to which a tread area
portion is generated by the radial accelerometer secured to the
tyre (see FIG. 6(a)). The signal can be low-pass filtered, in order
to remove high-frequency components due to interaction between the
road and the tyre (see FIG. 6(b)). From the filtered signal, the
amplitude Pp of the signal peak can be measured. Preferably, the
peak amplitude value to be measured corresponds to the difference
between the maximum signal value and the minimum signal value.
Furthermore, the amplitude corresponding to the first peak can be
used, or the amplitude of the second peak, or an average of the
first and of the second peak.
In order to derive the rotation speed of the tyre, the average
acceleration level a in a portion outside the signal variation
caused by the passage of the accelerometer under the contact patch
can also be measured. The radius of the tyre should also be known
for the above purpose. In an alternative embodiment, the average
signal value in a whole turn of the tyre could be used as a measure
of the average acceleration level a. In a further alternative
embodiment, using a plurality of sensor devices located within the
tyre at different circumferential positions, a first sensor device
located outside the contact patch could be used in order to measure
the average acceleration level a (and derive the rotation speed of
the tyre), in real-time, in the same time interval in which a
second sensor device passes under the contact patch. Simple control
electronics can be implemented within the sensor devices in order
to trigger the needed measurements. The needed algorithms for the
above described analysis of the signal generated by the
accelerometer can also be stored within the memory of the sensor
device, in order to be used by the associated processing unit.
The pressure p is also measured during running of the tyre. By
using the measured pressure p, the correct set of fit coefficients
of the tyre load curves can be identified (see equations [2]).
Should the measured pressure px be different from the pressure
values p1, p2, . . . pn used for the characterization of the tyre,
a corrective factor can be applied. Let, for example, p1 be the
closer stored pressure value to px, then the corrective factor may
be .gamma.=px/p1, so as the corrected fit coefficients take the
following values: pressure px: [(a1.sub.q1,p1).sup..gamma.,
(b1.sub.q1,p1).sup..gamma., (c1.sub.q1,p1).sup..gamma.], . . . ,
[(an.sub.qn,p1).sup..gamma., (bn.sub.qn,p1).sup..gamma.,
(cn.sub.qn,p1).sup..gamma.]
Then, by using the measured rotation speed V.sub.m (or
.omega..sub.m) and the identified fit coefficients, different
expected radial deformation peak values y.sub.--1(.omega..sub.m,
q1, px), y.sub.--2(.omega..sub.m, q2, px), . . . ,
y_n(.omega..sub.m, qn, px) can be determined. Such values
y.sub.--1, y.sub.--2, . . . , y_n are then compared with the
measured peak amplitude Pp, in order to the determine the closer
value thereof. Such closer value identifies the closer tyre load
curve, i.e. the closer tyre load to the actual load supported by
the tyre. The identification of the closer tyre load curve could be
enough for an estimation of the tyre load, depending on the
requirements. For a more precise determination, a simple proportion
can be performed in order to determine the actual tyre load. Let
y.sub.--3(.omega..sub.m, q3, px) be the closer expected peak
amplitude value calculated at px and V.sub.m(or .omega..sub.m),
identifying the closer tyre load q3. Thus, it holds: actual tyre
load: Pp=q3: y.sub.--3 and then: actual tyre
load=Pp.times.q3/y.sub.--3 [3]
The above described formulas for calculation of the actual tyre
load can also be stored within the memory of the sensor device, in
order to be used by the associated processing unit.
EXAMPLE
The Applicant has performed a series of measurements by using a
radial accelerometer secured to the inner liner of a tyre model
Pirelli.RTM. P7.RTM., having a radius of 0.31 m. FIG. 7 shows a
plot with four curves of the radial deformation peak values
measured during the characterization step, versus the rotation
speed of the tyre. The four curves shown in FIG. 7 refer to
measurements performed at an inflation pressure of 2.2 bar, and at
the following tyre loads: tyre loads of 250 kg, 300 kg, 450 kg, 600
kg. As above described, higher tyre loads correspond to higher
curves (i.e., to higher peak values). In particular, the four
curves shown in FIG. 7 can be described by the following fit
functions: y.sub.--1=0.034 .omega..sup.2+0.031 .omega.+0.27 for
q1=250 kg y.sub.--2=0.041 .omega..sup.2+0.049 .omega.+0.30 for
q2=300 kg y.sub.--3=0.049 .omega..sup.2+0.053 .omega.+0.23 for
q3=450 kg y.sub.--4=0.055 .omega..sup.2+0.030 .omega.+0.29 for
q4=600 kg [4]
After the characterization, a measurement at a tyre load different
from the above values was performed. From the radial acceleration
signal, a radial deformation peak amplitude value of 210 g and a
rotation speed of 75 km/h were derived. The inflation pressure was
2.2 bar.
By using equations [4], the following expected deformation peak
amplitudes can be calculated at a rotation speed of 75 km/h:
y.sub.--1=156 g; y.sub.--2=189 g; y.sub.--3=225 g y.sub.--4=251 g.
Thus, the closer peak amplitude value is y.sub.--3, corresponding
to a tyre load of 450 kg. By using equation [3], it could be
derived the actual tyre load, i.e. 420 kg.
It has to be understood that the above described method for
determining the tyre load could be modified without departing from
the general teachings of the invention. For example, a database
comprising values of expected radial deformation peaks
corresponding to predetermined tyre inflation pressures, tyre
rotation speeds and tyre loads intervals can be stored within the
memory of the sensor device 3, in place of the above mentioned fit
coefficients. The values stored in the database could be inferred
by characterization curves obtained as disclosed above. From such
database, an estimation of the tyre load could be done, after
having gained knowledge of the radial deformation amplitude, of the
tyre rotation speed and of the tyre inflation pressure.
The real-time determination of the load acting on a tyre mounted on
a vehicle is an important parameter that can be passed to a vehicle
control system, in order to control the behavior of the vehicle,
particularly in critical conditions. A vehicle control system may
comprise a brake controller (for example, an anti-lock brake unit),
and/or a steering controller, and/or a suspension controller,
and/or an engine controller, and/or a transmission controller.
For example, a vehicle brake control system may adjust the braking
force on each tyre according to the load on the tyre.
As another example, the loads on each tyre may be used to determine
the vehicle stability envelope and to select the maximum variation
allowed from steering commands. This information may be applicable
to a steering control system (Electrically Assisted Steering
Systems) to limit the yaw rate.
As another example, a vehicle suspension control system may adjust
the stiffness of the suspension springs for each tyre according to
the load on the tyre. Furthermore, a sensed unequal load
distribution between left fitted tyres and right fitted tyres could
be compensated by an Active Roll Control system, that currently use
sensed lateral acceleration to increase the hydraulic pressure to
move stabilizer bars, in order to remove a vehicle lean when
cornering.
The conditions of the vehicle may indicate that the performance of
the vehicle is reduced and that the driver should restrict his
driving maneuvers. The vehicle control system itself can take
action, for example in order to limit the maximum vehicle speed to
maintain stability and not exceed the tyre specifications, or to
limit steering yaw rate in order to keep rollovers from occurring.
The driver may be alerted to the current vehicle control system
condition and of the actions that the vehicle control system has
taken on his behalf to safe the vehicle (reducing the maximum
attainable speed, steering rate, engine power), as needed on a
display device. On the same display device it may also be shown
whether he should take further action on his own (change the
distribution of mass, restrict driving maneuvers and speed). The
display device may comprise a visual and/or an audible unit, for
example located in the dashboard of the vehicle.
* * * * *